Zen's older brother and the king of Clarines. Zen's relationship with his older brother is complex, but it is clear that he greatly respects Izana. As a child, Zen looked up to Izana and wished to be like him, but has since become aware of Izana's manipulative and mocking personality, which strains their relationship. While he respects Izana's ability to rule, Zen prefers respectful, open discussion and honest proceedings, as opposed to his brother's style of pulling the strings behind the scenes. As Shirayuki comes to hold a bigger part of Zen's life, Izana's meddling in their relationship frustrates him. While Zen openly admired his brother as a child, his current interactions with Izana are very formal in nature.
Zen's mother and queen dowager of Clarines. She cares for both her sons even if she can't see them very often.
Zen's relationship with Shirayuki began when he stumbled upon her in a forest while he was sneaking away from the castle. Upon seeing her, he noticeably got distracted by her beauty and ended up injuring his arm. He begins to question her as to why she is in the forest, and when she asks to heal his wound, he mistakes her for a suspicious individual who wishes to harm him, suggesting the medicine might be poison. Upon hearing this Shirayuki is struck by Zen's rudeness, but nevertheless harms her own arm with Zen’s sword and uses the medicine she was going to put on his wound saying, "It's not my hobby to carry poisons around with me”. Chastened, Zen laughs as his opinion of her completely changes and he gladly accepts the offer of her treating his wound.
After Shirayuki moves to Clarines, Zen spends more and more time with her and comes to greatly respect Shirayuki's dedication and responsibility, as well as her positive outlook on life, which inspires him to work harder. Meanwhile, Shirayuki thinks very highly of him too, as he represents what a good prince should be. As time went on, they began to fall in love with each other. As seen in the Lion of the mountain, he finally admitted he was in love with Shirayuki.
Zen was the first person to convey his feelings as he kissed her unexpectedly while they were talking alone. Though both are extremely embarrassed, Zen tells Shirayuki that the next time he touched her he would like to know what she thought. Later, he tells Mitsuhide that he has held feelings for Shirayuki for a long time. Eventually, Shirayuki makes her own feelings clear. Zen then asked her if she would take his hand, and she says yes. There, they began their relationship as lovers; however it is not public knowledge yet.
Mitsuhide is Zen's close aid and his best friend. Although they took some time to warm up to each other, they trust each other a lot now. Mitsuhide is said to be the only person Zen listens to.
Kiki is another aide and best friend of Zen. She worked for Zen for 6 years. And shows loyalty towards Zen as well as respecting him a lot. She seems to be an expert in playing chess, seeing as she defeats Zen and Mistuhide many times. Kiki is also helping to get Zen and Shirayuki together. She asks whether he wants Shirayuki to be his queen.
After being captured for threatening Shirayuki, Obi proclaims himself as Zen's servant, calling him "Master". While Zen is initially unhappy about this arrangement, being understandably mistrustful of him. However, Zen eventually comes to trust him greatly, to a level that he will leave Shirayuki in Obi's protection when he cannot be by her side. He is still occasionally exasperated by Obi, since he enjoys teasing Zen.